1. Field
The present disclosure relates to an apparatus and method for anaerobic wastewater treatment with a membrane, and more particularly, to an apparatus and method for anaerobic wastewater treatment with a membrane, which effectively generates biogas and suppresses fouling on a membrane surface by performing anaerobic treatment to wastewater and also efficiently performs biological treatment and membrane separation simultaneously under an optimal condition.
2. Description of the Related Art
Recently, a membrane bioreactor (MBR) is frequently applied in sewage and wastewater treatment. The membrane bioreactor treats wastewater with high efficiency by applying a membrane to a biological treatment process represented by an activated sludge, and the microorganism concentration in the reactor may be maintained high regardless of the sludge settleability. Therefore, the membrane bioreactor may have a compact design, allow high organic loading, and give high effluent quality. In particular, due to the compact design and advantageous energy efficiency, a submerged-type membrane bioreactor configured to directly immerse membranes in an aeration tank and suck out treated water is frequently applied. This method is disclosed in Korean Patent Registration No. 315968, Korean Unexamined Patent Publication Nos. 2000-0065883, 2000-0003714, 2002-0089255, 2003-0039038 or the like.
If such a submerged-type membrane bioreactor is applied, the membrane is inevitably clogged due to the foulant on a membrane surface. In order to prevent this phenomenon, turbulence is formed by means of aeration. However, in this case, the amount of aeration required for the biological treatment is much greater than the amount of air required, which results in excessive energy consumption and high maintenance costs.
In order to remedy the above shortcomings, in a paper <K. H. Ahn, K. G. Song, I. T. Yeom, K. Y. Park, (2001). “Performance comparison of direct membrane separation and membrane bioreactor for domestic wastewater treatment and water reuse,” Water Science & Technology: Water Supply, 1 (5-6), 315-323> and Korean Unexamined Patent Publication No. 2007-0075947, a membrane module equipped with a rotating disk or propeller is used to suppress the clogging of the membrane. However, in this method, in order to suppress the clogging of a membrane, it is needed to accelerate the rotation of the rotating disk or propeller to form turbulence effectively. Therefore, energy consumption is still required for rotating the rotating disk or propeller.
Meanwhile, the biological treatment of wastewater generally uses aerobic treatment which needs to supply oxygen, but the aerobic treatment consumes a lot of energy to supply oxygen. In comparison, the anaerobic treatment does not need to supply oxygen and produces available renewable energy by generating biogas. However, for the anaerobic treatment, it is important that anaerobes growing relatively slowly are maintained at a high concentration in a reactor. This may be solved by providing attached growth media where the anaerobes may be attached and grow and simultaneously using a membrane bioreactor. Therefore, Korean Patent Application No. 2012-0114781 proposes an efficient anaerobic membrane bioreactor which combines advantages of the anaerobic treatment and advantages of the attached growth media and the membrane bioreactor.
Since the basic condition of the anaerobic membrane bioreactor is the use of anaerobes, the anaerobic condition must be maintained. Therefore, perfectly blocking an external air is one of important factors, when determining the efficiency of the anaerobic treatment. However, in case of an anaerobic membrane bioreactor disclosed in Korean Patent Application No. 2012-0114781, a bioreactor taking charge of biological treatment and a membrane for separating treated water are combined with a single reactor. When exchanging or repairing parts of the membrane due to malfunction or the like, the reactor should be opened and contact the external air. Therefore, it is impossible to maintain perfect blockage from the external air, which may become a serious obstruction to the anaerobic treatment. In addition, in this case, operating conditions for biological treatment and membrane separation should be harmonized. However, if operating conditions such as residence times for efficient operation are different from each other, the biological treatment efficiency or the membrane separation efficiency may deteriorate. Therefore, it may be impossible to ensure efficient operation due to such a disharmonized state.